The present invention generally relates to implantable cardiac stimulation devices, and in particular, a stimulation device capable of discriminating among various atrial and ventricular arrhythmias and delivering high voltage shocks to treat such arrhythmias.
An ICD device is a particular type of cardiac stimulation device, which recognizes ventricular tachycardia (VT), ventricular fibrillation (VF) and other arrhythmias, and delivers high voltage electrical therapy to terminate such arrhythmias.
ICD devices have met with wide success in the detection of arrhythmias and in the administering of high voltage shocking therapy in response thereto, yet considerable room for improvement remains. In particular, many ICD recipients also suffer from supraventricular tachycardias (SVT), that is, an arrhythmia whose origin is above the ventricles and is conducted to the ventricles. The true underlying arrhythmia in these cases is often atrial fibrillation (AF), sinus tachycardia (ST), or other supraventricular tachycardias (SVTs), such as ectopic atrial tachycardia, atrial reentry, A/V nodal reentry, and paroxysmal atrial fibrillation or flutter. The SVT symptoms typically correspond to a heart rate, which is in a xe2x80x9clow tachycardia ratexe2x80x9d zone normally associated with VT.
These ICD patients may receive inappropriate therapy if the implanted device is not capable of reliably discriminating between VT and SVT and inappropriately classifies the rhythm as VT. It is unlikely that these arrhythmias would respond to ventricular therapy, and application of such therapy may accelerate an existing arrhythmia or induce additional arrhythmias.
ICD devices capable of dual-chamber sensing often provide better discrimination between the various types of arrhythmias than single-chamber ICD devices. However, even in dual-chamber ICD devices, it remains difficult to discriminate between VT""s with 1:1 retrograde conduction (VT 1:1), and SVT""s with 1:1 conduction (SVT 1:1), or ST""s. Other arrhythmias that may need to be discriminated one from the other include VT""s without 1:1 retrograde conduction (VT not 1:1), high rate VT""s (VTH), SVT""s without 1:1 conduction (SVT not 1:1) and atrial flutter (AFL).
Even in circumstances where the ICD ultimately administers the correct therapy, initial errors in discriminating between the various types of arrhythmias often results in one or more intervals lapsing before therapy is administered. For example, some ICD devices discriminate between different arrhythmias by making a preliminary classification as to the type of the arrhythmia, if any, associated with each individually detected event (e.g. P-waves, R-waves, etc.) and then counting each type of event using a set of running totals. A predetermined threshold is associated with each running total. The ICD device does not make a final decision as to the type of arrhythmia until the threshold of one of the running totals is exceeded. The ICD device administers therapy appropriate to that arrhythmia.
For example, if the threshold is programmed to twenty counts and the running total for events given a preliminary classification of VT reaches twenty counts, the stimulation device identifies the arrhythmia as being a VT arrhythmia and administers appropriate therapy at that time. Unfortunately, because of the difficulty in discriminating among events associated with different types of similar arrhythmias, the wrong running total may occasionally be incremented, thereby delivering inappropriate therapy for the true underlying rhythm or delaying appropriate therapy for the underlying rhythm.
Hence, there is a need for an improved ICD device which achieves a reduction in the occurrence of inappropriate VT therapy and which provides appropriate therapy more quickly. It is to these and other ends that the invention is primarily directed.
In accordance with a first aspect of the invention, a method for use with an implantable stimulation device connected to heart tissue is provided for discriminating various arrhythmias of the heart. As used herein, the term xe2x80x9cstimulation devicexe2x80x9d is used to cover all stimulation devices which may benefit from the use of the present invention for discriminating various arrhythmias, whether it is a pacemaker, cardioverter, defibrillator, a single-chamber or a dual chamber device, or a combination thereof.
In accordance with the method, a sequence of events are detected within the heart beginning at an initial point in time and a preliminary classification for each detected event is determined out of a plurality of heart rhythms. Running totals of the numbers of detected events within each of the predetermined classifications since the initial point in time are maintained along with sliding totals of the numbers of detected events within each of the predetermined classifications out of the most recent events. The arrhythmia of the heart is then determined based upon a combination of the running totals and the sliding totals.
In an exemplary embodiment, the implantable stimulation device is a combination ICD device which offers both atrial and ventricular pacing, and the plurality of heart rhythms includes normal sinus rhythm (NSR), ventricular fibrillation (VF), ventricular tachycardia without 1:1 retrograde conduction (VT not 1:1), ventricular tachycardia with 1:1 with retrograde conduction (VT 1:1), supraventricular tachycardias without 1:1 conduction (such as, atrial fibrillation (AF), atrial flutter (AFL), and other SVTs not 1:1) and supraventricular tachycardias with 1:1 conduction (either physiologic sinus tachycardia (ST) or a pathological SVT 1:1).
The determination of the patient""s heart rhythm, based upon a combination of the running totals and the sliding totals, is performed by first determining whether the sliding total of any one of the predetermined classifications exceeds a corresponding sliding total threshold. If so, the running totals of the predetermined classifications are selectively modified. Then, a determination is made as to whether the modified running total of any one of the predetermined classifications exceeds a corresponding running total threshold and, if so, the current state of the heart is identified as being the heart state corresponding to that predetermined classification and appropriate therapy is administered.
In one specific example, the running total for VF is selectively modified as follows. If the sliding total of the number of events having a preliminary classification of VF exceeds a corresponding sliding total threshold (such as, six out of the last eight events), then the running totals for ST, VT 1:1 and VT not 1:1 are added to the running total for VF. The running totals for ST, VT 1:1, VT not 1:1 and AF are then cleared.
In the exemplary embodiment, by adding the running totals for various preliminary classifications to other preliminary classifications based upon the values of the sliding totals, the stimulation device thereby biases the running totals using the sliding totals. The specific manner by which the running totals are biased is selected to help overcome common discrimination problems occurring in stimulation devices to thereby permit the stimulation device to make a correct and final therapy decision more quickly. For example, VF events are sometimes erroneously classified as being ST events, VT 1:1 events or VT not 1:1 events. Hence, as set forth in the example, the running totals for ST, VT 1:1 and VT not 1:1 are added to the running total for VF whenever at least six of the last eight events were identified as being VF events. Thus, if such an erroneous classification occurred, it is compensated for by adding the erroneous counts to VF counts. If no such erroneous classification occurred, then even with the added counts the running total for VF will not likely exceed the corresponding threshold and erroneous therapy will not be administered.
In accordance with a second aspect of the invention, a method is provided for use with an implantable stimulation device connected to heart tissue for determining a classification for an event detected within the heart, wherein the heart rate is between an upper and lower predetermined heart rate threshold, and wherein the heart is in atrial/ventricular (AN) synchrony. Initially, if a P-R interval (associated with the event) is detected, then a determination is made as to whether the P-R interval is physiologic, that is, between a physiologic upper and lower predetermined P-R interval thresholds. If the P-R interval is not between the upper and lower predetermined P-R interval thresholds, then the event is identified as being associated with VT 1:1. If, however, the P-R interval is between the upper and lower predetermined P-R interval thresholds, then a further determination is made as to whether the P-R interval is stable. If the P-R interval is not stable, then the event is identified as being associated with VT 1:1. If the P-R interval is stable, the event is either ST or SVT 1:1 and receives a preliminary classification of xe2x80x9cSTxe2x80x9d (As used here and in the flowcharts, the designation of xe2x80x9cSTxe2x80x9d is arbitrary and intended to include both physiological sinus tachycardias and all other pathological supraventricular tachycardias which have 1:1 conduction, since in a ventricular shocking device, if either one is present, no therapy is provided. However, in one embodiment, additional discriminators could be added to distinguish between a physiological ST and a pathological SVT 1:1 and the device could further provide atrial shock therapy.).
Among other advantages, by evaluating whether the P-R interval is physiologic and by evaluating the stability of the P-R intervals, the implantable stimulation device is better able to discriminate between VT 1:1 arrhythmias and ST or SVT 1:1 arrhythmias.
This method for determining a classification for an event may be advantageously employed as part of the determination of the preliminary classification of events detected within the heart for use with the first aspect of the invention.
In accordance with a third aspect of the invention, a method is provided for use with an implantable stimulation device connected to heart tissue for determining a classification for an event detected within the heart, wherein the heart rate is detected between an upper and a lower predetermined heart rate threshold, but wherein the heart is not in AV synchrony. Initially, an atrial rate and a ventricular rate are detected. A determination is made as to whether the atrial rate exceeds the ventricular rate, and if it does not, the event is identified as being associated with VT not 1:1. However, if the atrial rate does exceed the ventricular rate, then a determination is made as to whether an R-R interval associated with the event is stable. If the R-R interval is not stable, the event is either atrial fibrillation (AF), atrial flutter (AFL) or SVT not 1:1 and receives a preliminary classification of xe2x80x9cAFxe2x80x9d. (The designation of xe2x80x9cAFxe2x80x9d, as used here and in the flowcharts, is arbitrary and intended to include atrial fibrillation and atrial flutter and all other supraventricular tachycardias without 1:1 conduction, since in a ventricular only shocking device, no therapy is provided. However, in one embodiment, additional discriminators could be added to distinguish between atrial fibrillation from atrial flutter and other SVTs not 1:1, and the device could further provide atrial shock therapy.)
If, however, the R-R interval is stable, a further determination is made as to whether an R-P interval associated with the event is stable. If the R-P interval is not stable, the event is both AF and VT not 1:1 and receives a preliminary classification of VT not 1:1. (In this instance, in a ventricular shocking device, you would treat the VT. However, in a device, which also provides atrial therapy, the priority would be to treat the VT first, wait to see if the AF also resolves and, if it does not, then treat the AF.).
If, however, the R-P interval is stable, the event is AF, AFL or SVT not 1:1 and receives a preliminary classification of AF. (Again, in a ventricular shocking device, the designation of AF is arbitrary since in each case (AF, or SVT not 1:1), no therapy is provided.) Among other advantages, by evaluating the stability of the R-R and the R-P intervals, the implantable stimulation device is better able to discriminate VT not 1:1 arrhythmias from supraventricular tachycardias such as atrial fibrillation (AF), atrial flutter (AFL), and other supraventricular tachycardias that do not have 1:1 conduction (SVT not 1:1).
This method for determining a classification for an event also may be advantageously employed as part of the determination of the preliminary classification of events detected within the heart for use with the first aspect of the invention.
Other objects and advantages of the invention are achieved as well. Apparatus embodiments of the invention are also provided.